Combination reforming process

ABSTRACT

A conventional reforming catalyst, such as platinum-alumina, is used in the initial zone or reactors in a catalytic reforming process; the tail zone or reactors contains a supported group VIII bimetallic catalyst with platinum as one of the metallic components. In a preferred embodiment, the tail zone contains a platinum-iridium catalyst on a porous support such as alumina. In the tail reactors, conversion of paraffins is of primary importance, along with dealkylation of alkylbenzenes; in the initial reactors the predominant reaction is the conversion of naphthenes to aromatics. The combination process results in a significantly greater octane number product than is obtained in a conventional reforming process in which platinum-alumina catalyst is used throughout.

[72] Inventor Robert H. Kozlowski, Berkeley, and

Robert P. Sieg, Piedmont, both of Calif. [21] Appl. No. 865,011 [22] Filed Oct. 9,1969 [45] Patented Dec. 14,1971 [73] Assignee Chevron Research Company, San Francisco, Calif.

[54] COMBINATION PROCESS OF CATALYTIC REFORMING AND EXTRACTION 4 Claims, 1 Drawing Fig.

[52] US. Cl 208/93, 89 1 3 8 [51] Int. Cl C10g /08 Field of Search 208/15, 80, 89, 92,93,138

[56] References Cited UNITED STATES PATENTS 2,914,457 11/1959 Beavon H 2 :/9 6

2,921,015 1/1960 Shiras 208/ 3 ,030,299 4/1962 Plummet 208/96 3,044,950 7/1962 Swartz 208/93 3,110,661 11/ 1963 Franz 208/60 3,242,066 3/1966 Myers 208/93 3,415,737 12/1968 Kluksdahl 208/138 Primary Examiner- Herbert Levine Att0rneysA. L. Snow, F. E. Johnston, G. F. Magdeburger,

C. J. Tonkin and Dix A. Newell ABSTRACT: Increased yields of gasoline and jet fuel can be obtained from a feed boiling from to 550 F by fractionating the feed into two streams, reforming the lowerboiling stream at low pressure to produce a gasoline product, solvent extracting the higher-boiling stream to produce a raffinate and an extract, blending the extract with the gasoline product from the reforming zone, and using the raffinate for jet fuel.

COMBINATION PROCESSAOF CAIALY'HC.

REFORMING AND EXTRACTION BACKGROUND OF THE INVENTION W Field The present invention relates to a reforming process operated at low pressure. More particularly, the present invention is concerned with a combined low-pressure reforming process and solvent extraction process for producing high yields of gasoline and jet fuel materials.

Prior Art Over the years there has been a growing demand fox both gasoline and jet fuel products. As a result, numerous refining operations have been devised to optiinize the yields of either gasoline or jet fuel and minimize the production of light boiling range materials. Reforming processes for upgrading naphtha feedstocks have received significant emphasis over the years; also various hydrocracking processes for optimizing jet fuel production have been developed. Studies of methods for extracting the aromatic portions of feedstocks for use in gasoline from the nonaromatic portions have also been undertaken. The combination of reforming and solvent extraction has also received attention. For example, in U.S. Patent 3,044,950 it is disclosed that increased gasoline yield can be obtained by distilling a hydro-- genated catalytic cracking feedstock into at least two streams, a higher boiling stream and a lower boiling stream, solvent extracting the higher-boiling stream to obtain an aromatic portion and a nonaromatic portion, combining the nonaromatic portion with the lower boiling stream from the distillation zone and catalytically reforming the blend, then combining the effluent from the catalytic reformer with the? aromatic fraction from the solvent extraction zone. Also, in LLS Patent 2,914,457 the solvent extraction of the! effluent from a reforming zone is disclosed as having certain advantages; e.g., the aromatic extract can be used for gasoline and the paraffinic raffinate used as a diesel or jet fuel component. Alternately, the paraffinic portion can be recycled to the reformer.

SUMMARY OF THE INVENTION It has now been discovered that a significant increase. in total gasoline and jet fuel components from a 150 to 550 F feed can be obtained by: (l) fractionating the feed into at least two streams, a first stream boiling within the range of from 150 Fto 340 F, and a second stream boiling within the range from 300F to 550F; (2) reforming the first stream in a reforming zone in the presence of hydrogen at reforming conditions including a pressure of less than about 300 psig and preferably less than 200 psig, using a catalyst comprising a platinum group component associated with a porous solid carrier, preferably a platinum-containing catalyst having rhenium associated therewith; (3) solvent extracting the second stream to produce an extract enriched in aromatics and a raffinate enriched in nonaromatics and blending at least a portion of the extract with the high-octane gasoline product from the reforming zone and using at least a portion of the raffinate as a jet fuel component.

As a result of the combined reforming-solvent extraction DESCRIPTION OF THE INVENTION The feed used to produce high yields of gasoline and jet fuel products by means of the present invention should boil within the range from 150 to 550 F, preferably between 150 to 450 F. The feed may be a straight-run naphtha, a thermally cracked naphtha, a catalytically cracked naphtha, a hydrocrackate, or blends thereof.

Prior to fractionating the feed into the two streams, it may be advantageous to hydrofine the feed to reduce the sulfur content or to hydrogenate olefinic components. Hydrogenating the feedstock in a presaturation zone is generally accomplished by contacting the feed with a hydrogenation catalyst which is resistant to sulfur poisoning. A suitable catalyst for the hydrofining process, or hydrodesulfurization process, as it is sometimes referred to. is, for example, an alumina-containing support having associated therewith a minor proportion of molybdenum oxide and cobalt oxide. Other suitable hydrofining catalysts include nickel-molybdenum or nickel-cobalt-molybdenum supported on an alumina carrier or a zeolite carrier or combinations thereof. The catalyst can be pretreated with hydrogen sulfide prior to contact with the feed.

Hydrofining or hydrodesulfun'zation is generally conducted at a temperature within the range 700 to 850 F, a pressure of from 200 to 2000 psig, and a liquid hourly space velocity of from 1 to 5. The hydrofining is accomplished in the presence of hydrogen. Generally the hydrogen-to-feed ratio will be from 1000 to 5000 SCF of hydrogen per barrel of feed. The reaction conditions are generally severe enough to convert substantially all the organic sulfur to hydrogen sulfide. Preferably, the reaction conditions should be severe enough so that the effluent from the hydrofining zone contains less than about 10 ppm organic sulfur, preferably less than about 5 ppm organic sulfur, and more preferably less than about 1 ppm organic sulfur. Any produced H 8 is removed from the feed, preferably prior to fractionation of the feed into the lower-boiling range stream and the higherboiling range stream.

The feed, preferably containing low amounts of sulfur and other poisons, is fractionated by conventional means known in the art into at least two streams, a first stream boiling within the range of from 150 F to 340}; and a second stream boiling within the range of from 300F to 550F. Thus, in a situation wherein the feed has an initial boiling point of 150 F and an end point of 450 F, the first stream could have a boiling range of 150 to 320 F, and the second stream a boiling range of 320 to 450 F. In the fractionation zone, if necessary, any H 8, water, or light hydrocarbon gases may be removed as a separate stream.

The lower-boiling range stream, that is, the stream boiling from within the range of from 150 to 340F is separately processed from the higher-boiling range stream. Thus, the first stream is contacted in a reforming zone in the presence of hydrogen at reforming conditions to produce high-octane gasoline. The reforming conditions include a temperature of from 600 to 1100F, preferably from 750 to 1050 F. The pressures will be less than about 300 psig, and preferably less than about 200 psig. Generally the pressure will be above atmospheric, for example, at least 25 psig. The

preferred pressure range is from 50 to 200 psig. The combinaprocess, the product on of light hydrocarbgn gases, that s,

Cit-hydrocarbons, is decreased. A decrease in the production of light gases represents an increase in the pfoductiqniof significantly more valuable gasoline and/or jet fuel' components.

DESCRIPTION OF THE DRAWING The process of the present invention will be more fully; Iein J eBe EL Y ts s. t9 !12s. star in J tion of the lower-boiling range stream and the low pressure reforming operation permits the production of high yields gf a rbo nsra ejr ductsa.

The temperature and pressure in the reforming zone can be correlated with the liquid hourly space velocity (LHSV) to favor any particularly desirable reforming reactions, as, for example, dehydrocyclization or isomerization or dehydrogenation. In general, the liquid hourly space velocity will be from 0.1 to 10, and preferably from 1 to 5.

A 'Ll'ierefggming process is conducted in the presence of separated from the reformate and recycled to the reaction 1 zone. Thus, extraneous hydrogen need not necessarily be added to the reforming process. However, if desired, ex-

traneous hydrogen may be used at some stage of the operation, as, for example, during startup. Regardless of the source of the hydrogen, the hydrogen can be introduced into the feed prior to contact with the catalyst or can be contacted simultaneously with the introduction of feed to the reaction zone. The hydrogen need not necessarily be pure hydrogen, but may contain light hydrocarbon gases in admixture therewith. Generally, when hydrogen is recirculated to the reaction zone. some light hydrocarbon gases will be recirculated with the hydrogen. While it is preferred that relatively pure hydrogen be used, difficulty and expense in purifying recycle hydrogen often prevents this from being the case. Hydrogen is preferably introduced into the reforming reactor at a rate which varies from 0.5 to moles of hydrogen per mole of feed,

The reforming conditions vary depending on the feed used, whether highly aromatic, paraffinic or naphthenic, and upon the desired octane rating of the product. Generally it is preferred that the reforming process be operated at high severity conditions, that is, conditions which will result in the production of a gasoline product having at least 90 Fl clear octane rating, and more preferably at least 95 F-l clear octane rating.

The reforming zone may consist of one reactor or several reactors containing a hydrogenation-dehydrogenation catalyst. Preferably the reforming zone will comprise several reactors, preferably at least three reactors, in series. The hydrocarbon feed is preheated and mixed with hydrogen and then passed through the plurality of reaction zones containing catalyst. Generally in all but the last stages the reactions are endothermic; hence the hydrocarbon feed passing between the reactors is reheated to the desired conversion temperature. Reformed hydrocarbons are recovered from the terminal reactor and hydrogen is separated therefrom and a portion thereof recycled to the reactorts).

The catalyst which finds use in reforming comprises a platinum group component associated with a porous solid carrier. Preferably the catalyst comprises a platinum group component, e.g., platinum, palladium, iridium, ruthenium, etc., supported with a porous inorganic oxide as, for example, alumina. The platinum group component will be present in an amount of from 0.01 to 3 weight percent and preferably 0.01 to 1 weight percent. The weight percent of the platinum group component is calculated as the metal regardless of the form in which it exists on the catalyst. The platinum group component embraces all the members of Group VIII of the Periodic Table having an atomic weight greater than 100 as well as compounds and mixtures of any of these. Platinum is the preferred component because of its better reforming activity,

Porous sdHiTam'ers wi'izrshaaaaana us f ofieform ing are generally the inorganic oxides, particularly inorganic oxides having surface areas of 50 to 750 m lgm, preferably.

150 to 750 m lgm. The carrier can be a natural or a synthetically produced inorganic oxide or combination of inorganic oxides. Typical acidic inorganic oxide supports which can be used are the naturally occurring aluminum silicates, particularly when acid treated to increase the activity, and the synthetically-produced cracking supports, such as silicaalumina, silica-zirconia, silica-alumina-zirconia, silicamagnesia, silica-alumina-magnesia, and crystalline zeolitic aluminosilicates.

It is generally preferred that the catalysts have low cracking activity, that is, have limited acidity. Thus, it is particularly preferred that alumina be present. Any of the forms of alumina suitable as a support for reforming catalysts can be used, e.g., gamma-alumina, eta-alumina, etc. Furthermore, alumina can be prepared by a variety of methods for purposes of this invention. Thus, the alumina can be prepared by adding a suitable alkaline agent such as ammonium hydroxide to a salt of aluminum, such as aluminum chloride, aluminum nitrate, etc, in an amount to form aluminum hydroxide which on drying and calcining is converted to alumina. Alumina may also be prepared by the reaction of sodium aluminate with a suitable reagent to cause precipitation thereof with the resulting formation of aluminum hydroxide gel. Also, alumina may be prepared by the reaction of metallic aluminum with hydrochloric acid, acetic acid. etc.. in order to form a hydrosol which can be gelled with a suitable precipitating agent, such as ammonium hydroxide. followed by drying and calcination.

Other components in addition to the platinum group component can be present with the porous solid carrier. It is particularly preferred that rhenium be present, for example, in an amount of from 0.01 to 5 weight percent and more preferably 0.01 to 2 weight percent. Regardless of the form in which rhenium exists on the catalyst, whether as metal or compound, the weight percent is calculated as the metal. Rhenium significantly improves the yield stability of the platinum-containing catalyst; that is, a process using a platinum-rhenium catalyst has a significantly lower yield decline throughout the reforming process than a catalyst comprising platinum without rhenium. The platinum-rhenium catalyst is more fully described in U.S. Patent 3,415,737, which is incorporated herein by reference thereto.

The catalyst comprising the platinum group component can be prepared by a variety of methods; that is, the platinum group component can be associated with the porous solid carrier by impregnation, ion-exchange, coprecipitation, etc. Generally it is preferred to incorporate the platinum group component by impregnation. When rhenium is incorporated along with the platinum group component, the rhenium component can also be associated with the carrier by various techniques, e.g., impregnation, ion-exchange, coprecipitation, etc. Preferably, the platinum group component and rhenium component are associated with the carrier by impregnation, either simultaneously or sequentially. Particularly preferred platinum group compounds for use in impregnation include chloroplatinic acid, ammonium chloroplatinates, polyammineplatinum slats, palladium chloride, etc. Suitable rhenium components are perrhenic acid, ammonium or potassium perrhenates, etc. W W

The catalyst used in reforming can be promoted by the addition of halides, particularly fluoride or chloride. Bromides may also be used. The halides provide a limited amount of acidity to the catalyst which is beneficial to most reforming operations. A catalyst promoted with halide preferably contains from 0.1 to 3 weight percent total halide content. Halides can be incorporated onto the catalyst carrier at any suitable stage of catalyst manufacture, e.g., prior to or following incorporation of the platinum group component and/or the rhenium component. Halide can also be incorporated onto the catalyst during incorporation of the platinum group component or rhenium component.

The second stream from the fractionation zone, that is, the feed stream boiling with the range of from 300 to 550 F, is passed to a solvent extraction zone in contact with a selective solvent for aromatic hydrocarbons which is relatively immiscible with nonarornatic hydrocarbons. The solvent should have relatively selective solubility for the aromatics at the elevated temperature of the extraction, preferably in excess of 200 F, and a low solubility at the temperature of operation of the desorbing procedure, generally in the neighborhood of F, wherein aromatics are separated from the solvent.

Various common selective solvents for aromatics, e.g.. phenol, nitrobenzene, the sulfolanes, acetonitrile, furfural, or one of the several g1 ycols may be used. A preferred solvent is diethylene glycol, which may be used alone or diluted with, say, 2 to 10% by weight of water. Representative of others of the glycol solvents which may be utilized with somewhat less advantageous results are ethylene glycol. triethylene glycol, tetraethylene glycol and dipropylene glycol. The particularly preferred solvents are the sulfolanes. Among the suitable sulfolanes are sulfolane itself and many of its derivatives, such as hydrocarbon-substituted sulfolanes, including alkyl sulfolanes, e.g., 3-methylsulfolane, preferably containing not more than 14 carbon atoms; hydroxy sulfolanes such as 3-sulfolanol, 3-methyl-4-sulfolanol, etc.; sulfolanyl ethers such as methyl-3-sulfolanyl ether; and sulfolanyl esters such as 3-sulfolanyl acetate.

1n the extraction zone there is formed an extract phase enriched in aromatics and a raffinate phase containing predominantly nonaromatic hydrocarbons. The extract phase or fraction upon its removal from the extraction zone is cooled to effect the formation of a solvent phase and a hydrocarbon phase. Other means can be used to extract the solvent phase and the aromatic phase as, for example, distillation. However, generally sufficient separation can be accomplished by cooling the extract mixture of aromatic and solvent. The aromatic phase may be water washed to remove final amounts of solvent.

The raffinate fraction from the solvent extraction zone is also generally water washed to remove any solvent dissolved therein, dried, and at least a portion thereof then used as a jet fuel component. The raffinate fraction will be enriched in nonaromatic components, that is. enriched in substantial amounts of paraffins, which make valuable jet fuel components.

At least a portion of the extract or aromatic fraction from the solvent extraction zone is blended with the product from the reforming zone to produce a high-octane gasoline product.

1n a preferred embodiment wherein sulfolane is used as the extraction medium, the feed to be extracted can be fed to a rotating disc contactor containing sulfolane. 1n the rotating disc contactor, both extraction of aromatics by the sulfolane and separation of the extract fraction and the raffinate fraction occur. The raffinate fraction is removed from the contactor and can then be further treated in another rotating disc contactor containing sulfolane to remove any remaining aromatics. Generally, this is not necessary for purposes of this invention. The raffinate fraction is generally passed from the rotating disc contactor to a water wash column to remove any sulfolane. At least a portion of the raffinate recovered from the water wash column can then be used as a jet fuel component. The extract fraction enriched in aromatics is recovered from the rotating disc contactor and then passed to a distillation column to remove sulfolane from the aromatics. At least a portion of the aromatics fraction may then be admixed with the gasoline fraction from the low pressure reformer. Sulfolane will generally be purified and recycled to the rotating disc contactor. It is not necessary for purposes of the present invention to use severe solvent extraction conditions, i.e., conditions to result in complete separation of aromatics from nonaromatics.

It may be desirable as a preferred embodiment of the present invention to reform the higher-boiling stream from the fractionation zone, prior to solvent extraction, in the presence of hydrogen with a catalyst comprising a platinum group component in association with a porous solid carrier at reforming conditions, including a pressure greater than about 300 psig, preferably greater than about 350 psig. For this particular embodiment, it is generally desirable that the feed to the high pressure reforming zone not exceed an end boiling point of about 450 F. The catalyst can be similar to the catalyst used in the low pressure reforming zone and and will preferably be a platinum-rhenium-alumina catalyst. The other reforming conditions are correlated with the pressure to produce a high-octane gasoline having at least 90 F 1 clear octane rating. The C,=. product from the high-pressure reforming zone can then be passed to the solvent extraction zone.

As a further embodiment of the process wherein the higher boiling stream from the distillation zone is reformed prior to extraction, it may be desirable to pass the raffinate fraction from the solvent extraction zone to a distillation column for separation into two fractions, ajet fraction boiling within the range from about 300F to about 450 F and a lighter fraction boiling below about 300 F, said jet fraction being used as a jet fuel component and said lighter fraction being blended with the gasoline product from the low-pressure reforming zone. The aromatics extract from the solvent extraction zone is still blended with the gasoline product from the low-pressure reforming zone.

The process of the present invention will be more fully understood by reference to the drawing in the Figure. A hydrocarbon feedstock boiling within the range from 150 to 550 F is passed by line 1 into hydrofining zone 2. The hydrofining zone will contain a catalyst, for example cobalt oxide and molybdenum oxide supported on alumina, and the reaction conditions will be such as to substantially convert any organic sulfur to H S. The hydrofining operation is conducted in the presence of hydrogen provided by means of line 3, and the hydrogen may come from the low-pressure reforming zone 4 or from any other hydrogen source.

The effluent from the hydrofining zone may be purified in a separation zone or distillation zone (not shown in the Figure). The hydrocarbon feed is then passed by line 5 to a fractionation zone 6 wherein it is separated into at least two streams, a first stream boiling within the range of from 150F to 340F and a second stream boiling within the range of from 300 to 550 F. The first stream is passed by line 7 to reforming zone 4 in contact with a platinum-group component catalyst at reforming conditions including a pressure of less than about 300 psig. Hydrogen is made available to the reforming zone by means of line 8. The hydrogen may be bottled hydrogen or hydrogen separated from the effluent from the reforming zone, etc. The second stream is passed by line 9 into solvent extraction zone 10 in contact with a solvent selective for aromatics, preferably sulfolane. The aromatic extract is removed from the solvent extraction zone by line 11 and is freed of solvent by conventional means (not shown in the Figure) and at least a portion passed into admixture with the effluent in line 12 from reforming zone 4. The blend is passed by line 13 to gasoline storage.

The raffinate fraction from the solvent extraction zone is recovered by line 14 and, after suitable treatment to remove any solvent dissolved therein (not shown in the Figure) is used as a component forjet fuel.

The process of the present invention will be more readily understood by reference to the following Example.

EXAMPLE The process of the present invention is compared with a process wherein only reforming at an elevated pressure occurs.

A feed boiling from 173 to 426F and containing 39 volume percent paraffins, 43.6 volume percent naphthenes and 17.4 volume percent aromatics, having an F-l clear octane rating of 52.5 and being essentially free of sulfur (less than 0.1 ppm) is reformed in the presence of a catalyst comprising platinum and rhenium in association with alumina. The platinum-rhenium-alumina catalyst comprises 0.3 weight percent platinum, 0.3 weight percent rhenium and 0.6 weight percent chloride, the remainder being alumina. The reforming process conditions include a feed rate, in barrels per day (BPD), of about 20,000, a liquid hourly space velocity of 1.5, a hydrogen to hydrocarbon mole ratio of 6, and a pressure of 500 psig. The reforming is run to produce a gasoline product having a F-l clear octane rating.

The results of the reforming process are tabulated under column A in the Table.

For the process of the present invention, a feed, substantially as described above, is fractionated in a distillation column into two fractions, a lower boiling range fraction and a higher boiling range fraction. The lower boiling range fraction boils from about 173 to 329F and contains 42.2 volume percent paraffins, 42.6 volume percent naphthenes. and 15.2 volume percent aromatics. The F-l clear octane rating is about 55. The lowerboiling fraction is then reformed in the presence of a platinum-rhenium-alumina catalyst containing 0.3 weight percent platinum, 0.3 weight percent rhenium, and 0.6 weight percent chloride, the remaining portion being alumina. The reforming conditions include a feed rate to the reformer of about 15,000 barrels per day (BPD), a liquid hourly space velocity of 2, a hydrogen to hydrocarbon mole ratio of 6, and a pressure of 200 psig. A product of about 100 F--] clear octane rating is produced.

The higher-boiling fraction from the distillation column boils within the range of from about 329 to 426 F. and is passed to a sulfolane extraction unit at a rate of about 5000 BPD. The extraction zone is a rotating disc contactor and is operated at a temperature of about 240 F. The solvent/ oil weight ratio is about 2.711. The amount of aromatics extract, after removal of sulfolane and drying, is about 1470 BPD of 77.6 volume percent aromatics content. This aromatics extract is combined with the gasoline product from the low pressure reformer. The amount of raffinate fraction from a sulfolane extraction zone, after treatment to remove any sulfolane, is about 3530 BPD of 2L3 volume percent aromatics content. The raffinate fraction is of good jet fuel quality having a 25 mm smoke point. The results of the combination of the low pressure reforming-solvent extraction process is tabulated under column B in the Table.

TABLE A B Reforming Reforming at 500 psi at 200 psi 12,360 (from Reformer) 1,470 (from Extract) 13,830 (Total) As is seen from the Table. reforming of the hydrocarbon feed at 500 psig results in a total liquid product of 16,000 BPD. On the other hand. the process ofthe present invention. combining reforming at 200 psig using a platinum-rhenium catalyst and solvent extraction. results in a total liquid product of 17.360 BPD. In both cases, a 20,000 BPD feed rate is involved. Thus. it it seen that by the process of the present invention. a significant increase in valuable liquid product is obtained. In this case. 1.360 extra barrels of valuable liquid product is produced.

The foregoing disclosure of this invention is not to be considered as limiting since many variations can be made by those skilled in the art without departing from the scope or spirit of the appended claims.

What is claimed is:

1. A process for increasing the yield of valuable gasoline and jet fuel products from a feed boiling within the range from F. to 550 F. which comprises:

(1) fractionating said feed into at least two streams.

a first stream boiling essentially within the range from 150 to 340 F., and a second stream boiling essentially within the range from 300 to 550 F.;

(2) reforming said first stream in a reforming zone in the presence of hydrogen at reforming conditions. including a pressure of about 25 to about 200 psig, using a catalyst comprising a platinum group component associated with a porous solid carrier, to produce high-octane gasoline;

(3) solvent-extracting said second stream without prior processing in a solvent extraction zone to produce a raffinate fraction enriched in nonaromatics and an extract fraction enriched in aromatics; I

(4) blending at least part of said extract fraction with the high-octane gasoline product from the reforming zone; and

(5) passing at least part of the raftinate fraction to jet fuel.

2. The process of claim 1 wherein said feed is hydrofmed at hydrofming conditions prior to fractionation.

3. The process of claim 1 wherein said reforming is conducted in the presence of a catalyst comprising a platinum component in an amount from 0.01 to 3 weight percent in association with alumina.

4. The process of claim 3 wherein said catalyst comprises rhenium in an amount from 0.01 to 5 weight percent. 

2. The process of claim 1 wherein said bimetallic catalyst is platinum-iridium.
 3. The process of claim 2 wherein said support is alumina.
 4. The process of claim 2 wherein said support contains halogen.
 5. In the catalytic reforming of a naphtha stock in the presence of hydrogen boiling in the range of 80* to 450* F. and comprising paraffins, naphthenes, and aromatics which comprises passing said feedstream into a plurality of catalytic reforming zones at catalytic reforming conditions wherein said initial zone contains a catalyst consisting essentially of platinum on a refractory inorganic oxide support and wherein said naphthenes are predominantly converted to aromatics in said initial zone and said paraffins are predominantly aromatized in the tail zones of said plurality of catalytic reforming zones, the improvement which comprises contacting effluent from said initial zone when it contains a maximum of about 10 weight percent of naphthenes with a supported bimetallic catalyst in a tail zone, said bimetallic catalyst consisting essentially of about 0.01 to 2.0 weight percent platinum and about 0.01 to 2.0 weight percent of a Group VIII metal selected from the group consisting of iridium, ruthenium and rhodium, and recovering a product of high-octane value.
 6. The process of claim 5 wherein said bimetallic catalyst comprises about 0.01 to 2.0 weight percent platinum, about 0.01 to 2.0 weight percent iridium and the remainder support.
 7. The process of claim 5 wherein said support contains halogen.
 8. The process of claim 5 wherein said reforming takes place at a temperature of 600* to 1,050* F.
 9. The process of claim 8 wherein said reforming takes place at a pressure of 15 to 600 p.s.i.g.
 10. The process of claim 9 wherein said reforming takes place in the presence of a hydrogen recycle of 1,000 to 10,000 standard cubic feet per barrel of naphtha feed.
 11. The process of claim 9 wherein said naphtha is charged into said catalytic reforming zones at a weight hourly space velocity of 0.5 W/hr./W to about 10 W/hr./W, based on the total amount of catalyst in the system.
 12. A process for catalytically reforming a hydrocarbon feedstream, in the presence of hydrogen, boiling between about 80* to 450* F. and containing 15 to 75 weight percent naphthenes, 15 to 75 weight percent paraffins and the remainder aromatics, which comprises passing said feedstream and a hydrogen-rich gas at a temperature of 600* to 1,050* F., a pressure of 15 to 600 p.s.I.g., at a space velocity of 0.5 to 10 W/hr./W, into a first catalytic reforming zone, said zone comprising a catalyst consisting essentially of platinum on a refractory inorganic oxide support, whereby the naphthene content is decreased to a maximum level of about 10 weight percent, passing the effluent from said first zone into a second catalytic reforming zone, said second zone containing a bimetallic catalyst which consists essentially of 0.01 to 2.0 weight percent of platinum and 0.01 to 2.0 weight percent of a Group VIII metal selected from the group consisting of iridium, ruthenium and rhodium on a refractory inorganic oxide support, and recovering a product of high-octane number.
 13. The process of claim 12 wherein said bimetallic catalyst comprises platinum and iridium on a refractory support.
 14. The process of claim 13 wherein said support contains halogen.
 15. The process of claim 13 wherein said support is alumina.
 16. The process of claim 13 wherein said support comprises 0.01 to 2.0 weight percent platinum and 0.01 to 2.0 weight percent iridium. 